The present invention relates generally to zoom spotlight illuminating apparatuses that provide a spot beam of variable size and beam angle, and specifically to a zoom spotlight apparatus that uses a multiple wavelength light emitting diode (LED) array and its accompanying optical elements.
Spotlights have long been used in a variety of applications where a narrow beam angle is desired or preferable. In theatrical lighting, a spotlight is often used to brightly illuminate a performer or small group of performers on a stage. In photography and other studio applications, a spotlight may be used to brightly illuminate a selected small area. The narrow beam angle of a typical spotlight provides greater light intensity over a small area, compared to a floodlight of similar total light output, but with wider beam angle. Desired attributes of a spotlight include uniform light intensity within the area of illumination, which may also translate to a sharp demarcation between the illuminated and non-illuminated areas. In other words, the beam of the spotlight should have a well-defined boundary, with even illumination within the beam. In addition, the spectral distribution within the beam should be highly uniform, without visible color variation. This includes the avoidance of fringing effects, such as color differences around the perimeter of the spot beam. Additional desirable attributes for some spotlight applications include the ability to vary the color of the spot beam, as well as the ability to vary the color temperature of white light.
Zoom spotlights provide the additional functionality of an adjustable spot beam size, with variable beam angle. At a given distance from the area to be illuminated, a preferred zoom spotlight would provide a usefully wide range of spot beam size, while maintaining a highly uniform intensity of illumination within the beam. The zooming capability is ideally provided without compromising the other attributes of a fixed spotlight.
Prior art zoom spotlights typically make use of some form of incandescent bulb as a light source. High-intensity discharge (HID) bulbs are frequently used, based on their higher luminous efficacy when compared to a tungsten-filament incandescent bulb. Differing types of HID bulbs may be used, depending on the desired light output, correlated color temperature of the light output, color rendering index, bulb lifetime, cost, and other attributes. A desirable attribute of most incandescent and HID bulbs is that their light is emitted from a small area, so that the bulb provides a reasonable approximation of a point source of light. This simplifies the design of the optical elements needed to provide the adjustable spot beam.
The optical elements of a typical prior art zoom spot light may include reflectors, light scramblers or randomizers, apertures, and one or more lenses. The mechanisms for adjusting beam spot size and angle, while maintaining a uniform beam with well-defined boundaries, may involve movement of the bulb within a reflector, varying the size and/or position of an aperture that is placed in front of the bulb, and/or varying the position of one or more lenses that are used to collect the light from the bulb, as well as to focus or collimate the light.
Although bulb-based zoom spotlights are capable of providing a bright, uniform spot beam of varying size and beam angle, the use of incandescent (or HID) bulbs has some significant disadvantages. Incandescent and HID bulbs have a relatively short lifetime, especially at higher levels of light output, and require frequent bulb replacement. Significant heat is generated, and the electrical power requirements are high. For a given type of bulb, the spectral content of the beam is basically fixed, so that external filters are needed to either provide light of a different color, or to modify the color temperature of the light. Such color filters add cost and complexity to the lighting system, and also significantly reduce the efficiency of the light, by filtering out a portion of the bulb's output.
Luminaires based on Light Emitting Diodes (LEDs) are becoming increasingly popular, due to rapid developments in LED technology, and increases in brightness and efficiency. LEDs have multiple advantages as a light source, including high reliability and long lifetime, especially when compared to incandescent bulbs and HID light sources. The cost per Watt of LED light sources is also decreasing rapidly, leading to broader applicability for a wider range of lighting applications. LED light sources are also able to provide multiple colors without the use of external filters or color wheels, including white light of different color temperatures.
However, prior art LED light sources still have significant disadvantages, especially for a zoom spotlight application. The light output of individual LEDs is insufficient for most applications. If the total light output is increased by grouping multiple individually-packaged LEDs, this results in a diffuse, spatially-separated collection of multiple light sources, with difficult optics. In order to form a uniform spot beam, a portion of the optics may need to be replicated for each of the individual LEDs, so that the light output from the multiple LEDs can be combined into a single, uniform spot beam.
The present invention's densely-packed array of LED chips addresses the disadvantages of prior art LED spotlights, while providing the general advantages of LED technology. The densely-packed LED array provides the light output of large numbers of LED chips, rivaling the light output of incandescent bulbs and HID lighting, while retaining the high reliability and long lifetime advantages of LEDs. Similar to many incandescent bulbs, the densely-packed LED array approximates a point source of light, acting as an “extended point source”.
The extended point source nature of the present invention's densely-packed LED array provides significant advantages to the application of zoom spotlights. A single set of optical elements can be used to direct the light output of the entire LED array, making it easier to form a uniform spot beam, with adjustable size and beam angle. The zoom spotlight optics can be largely based on prior art practice from zoom spotlights that use incandescent bulbs, with some variations. This greatly reduces the cost and complexity of the optical elements, compared to prior art LED zoom spotlights. The use of the densely-packed LED array, using LED chips of multiple wavelengths, also provides dynamic color-mixing capability, including the ability to vary the color temperature of white light. This can be accomplished using arrays containing red, green, blue, and sometimes amber LEDs, or “white” LEDs comprised of blue LED chips that are coated with phosphors that provide broader spectrum yellow and orange light. By avoiding the need for external filters or color wheels, the LED zoom spotlight of the present invention provides a significant advantage over prior art zoom spotlights.